Announcing her resignation with a written statement, Boke said that the CHP, "which should be the strongest political actor representing 'No' will," has made controversial decisions questioning intra-party democracy, and suppressing opponents in the party.
She stated that the different ideas in the party were not included in the decision making processes and the party boards were not actively operated.
"As a politician who believes in the universal principles of participatory democracy [and] social democracy, and who thinks that the road to the libertarian democracy in Turkey is going through these values, I do not find it appropriate to be part of the existing administration's mentality," she said.
Boke added that she will continue to serve as a lawmaker in the parliament as a CHP party member.
Some in the party have been critical of CHP leader Kemal Kilicdaroglu over decisions made during last month’s campaign against wide-ranging constitutional changes.
Turkish voters narrowly endorsed an executive presidency in an April 16 referendum. The CHP had campaigned for a No vote.
On Wednesday, the CHP decided to call an ordinary party congress to elect the party’s new leader.
Kemal Kilicdaroglu has led the CHP since 2010. At the last year’s party congress, Kilicdaroglu was the only candidate for leader, winning 990 votes from 1,238 party assembly members.